/Engine/Plugins/Experimental/LandscapePatch/Source/LandscapePatch/Public/LandscapeTexturePatch.h
In addition, you may need to call SetHeightEncodingMode, SetHeightEncodingSettings, and SetZeroHeightMeaning based on how you want the data you write to be interpreted. This part is not specific to using an internal render target, since you are likely to need to do that with a TextureAsset source mode as well.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category=LandscapePatch) virtual [UTextureRenderTarget2D](API\Runtime\Engine\Engine\UTextureRenderTarget2D) * GetHeightRenderTarget ( bool bMarkDirty )